The invention relates generally to an intravascular catheter device for providing radiation to the interior walls of a human body lumen. More particularly, the invention relates to a catheter and method of use for selectively delivering radiation to portions of the walls of the human body lumen by distributing radioactive fluid non-uniformly within a catheter.
Intravascular diseases are commonly treated by relatively non-invasive techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA). These therapeutic techniques are well known in the art and typically involve use of a guide wire and catheter, possibly in combination with other intravascular devices. A typical balloon catheter has an elongate shaft with a balloon attached proximate the distal end and a manifold attached proximate the proximal end. In use, the balloon catheter is advanced over the guide wire such that the balloon is positioned across and adjacent a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened.
Vascular restrictions that have been dilated do not always remain open. In approximately 30% of the cases, a restriction reappears over a period of months. The mechanism of restenosis is not understood, but is believed to be different from the mechanism that caused the original stenosis. It is believed that rapid proliferation of vascular smooth muscle cells surrounding the dilated region may be involved. Restenosis may be in part a healing response to the dilation, including the formation of scar tissue.
Intravascular treatments, including delivery of radioactive radiation have been proposed as a means to prevent or reduce the effects of restenosis. For example, U.S. Pat. No. 5,199,939 to Dake et al. suggests that intravascular delivery of radiation may inhibit restenosis. Dake et al. suggest delivering radiation within the distal portion of a tubular catheter. Fischell, in the publication EPO 0 593 136 A1, suggest placing a thin wire having a radioactive tip near the site of vessel wall trauma for a limited time to prevent restenosis. Problems exist in attempting to provide uniform radiation exposure using a point or line source. Specifically, as the radiation varies inversely with the square of distance from a point source and inversely with distance from a line source, such sources laying off center near one vessel wall in a lumen may overexpose the nearby wall while underexposing the further away wall.
Bradshaw, in PCT publication WO 94/25106, proposes using an inflatable balloon to center the radiation source wire tip. In PCT publication WO 96/14898, Bradshaw et al. propose use of centering balloons which allow blood perfusion around the balloon during treatment. U.S. Pat. No. 5,540,659 to Tierstein suggests use of a helical centering balloon, attached to a catheter at points about the radiation source to allow perfusion through the balloon, and between the balloon and radiation ribbon source.
Use of continuous centering balloons having a beta radiation source within may significantly attenuate the beta radiation when the balloon is filled with inflation fluid. Further, the balloon may allow the radiation source to xe2x80x9cwarpxe2x80x9d when placed across curved vessel regions, allowing the balloon to bend but having the central radiation source lying in a straight line between the two ends. Segmented centering balloons may improve the warping problem but may also increase beta attenuation by allowing blood to lie or flow between the beta source and vessel walls. Balloons allowing external perfusion in general have the aforementioned beta attenuation problem.
Rather than attempting to center a line or point radiation source using centering balloons or the like, U.S. Pat. No. 5,616,114 to Thornton et al. suggests inflating a balloon with a radioactive fluid. The balloon is inflated until the outer surface of the balloon engages the vessel walls. This inflation process requires a substantial amount of radioactive fluid. In this configuration, the radiation emitted by a portion of the fluid, which is distant from the balloon surface, is attenuated before reaching the vessel walls.
In some cases, it may be desirable to provide non-uniform radiation exposure within a vessel, for example, when a lesion does not uniformly extend around the circumference of the vessel wall. For these cases, it may be advantageous to provide more radiation to some segments of the vessel wall and less radiation to others. What remains to be provided, then, is an improved apparatus and method for delivering radiation non-uniformly to vessel walls.
The present invention provides devices and methods for providing radiation non-uniformly or to selected areas around the circumference of a segment within a given segment of a human body vessel. This allows selected portions of a vessel within a given segment to have a higher radiation exposure than other portions. As indicated above, this may be advantageous when, for example, a lesion is not uniformly distributed around the circumference of a vessel wall.
In one illustrative embodiment, a catheter is positioned within a desired vessel, across and adjacent to a lesion. A radioactive fluid is then injected into the catheter. The catheter directs the radioactive fluid non-uniformly about the central axis of the vessel in the area of the lesion. In an illustrative embodiment, the radioactive fluid is directed to those portions of the vessel wall that have the lesion present, and away from those portions of the vessel wall that are free from the lesion.
It is recognized that a lesion can extend around the entire circumference of the vessel wall, but may be thicker in one area than in another. Accordingly, it is contemplated that different radioactive fluids may be directed to different portions of a lesion. By providing the proper type of radioactive fluid, a particular lesion may receive the proper radiation exposure, while reducing the exposure to other body tissue. A preferred radiation source is a beta emitter, as beta radiation penetrates only a few millimeters into tissue, rather than through the vessel tissue and into other body tissues as can be the case with gamma emitters. However, other radiation sources may also be used.
The catheter preferably includes a shaft with at least one infusion lumen therein, and a balloon member mounted on the distal end of the shaft. The balloon member preferably includes two or more inflatable channel members. Each of the inflatable channel members form part of the outer surface of the balloon member. Selected inflatable channel members are in fluid communication with the infusion lumen of the shaft. An injecting device is used to inject a radioactive fluid into selected inflatable channel members via the at least one infusion lumen. By aligning the selected inflatable channel members with the lesion, the lesion may receive the proper radiation exposure.
It is also contemplated that the shaft may include a second infusion lumen, and that some of the inflatable channel members may be in fluid communication with the second infusion lumen. By selectively injecting radioactive fluid into the appropriate infusion lumen, the proper inflatable channel members may be inflated to irradiate the corresponding portion of the lesion. It is contemplated that any number of separately filled inflatable channel members may be provided to accommodate a wide variety of lesion configurations.
It is further contemplated that some inflatable channels are designed for delivering therapeutic agents into portions of the lesions. These additional therapeutic agents may aid in the treatment of the lesion, or in counteracting the adverse effects of the radiation. Anti-angiogenic, anti-proliferative or anti-thrombogenic drugs are examples of such additional therapeutic agents. With this embodiment, at least one infusion lumen is included in fluid communication with selected drug delivery channel members on the balloon. These drug delivery channel members allow the drug to diffuse through the wall of the channel to the treatment site. The combination of radiation and drug therapy is believed to provide added benefits.
Alternatively, or in addition to, it is contemplated that different radioactive fluids may be injected into each of the infusion lumens to provide different radiation levels and/or radiation types. For example, the concentration of radioactive isotopes and/or the type of radioactive isotopes may be modified to provide a number of different radioactive fluids. By using more than one radioactive fluid, the inflatable channel members that are associated with one of the infusion lumens may exhibit different radiation characteristics than the inflatable channel members that are associated with another one of the infusion lumens. Finally, it is contemplated that the radioactive fluid may be maintained in each of the infusion lumens for different periods of time. This may provide another degree of flexibility in achieving a desired radiation dosage at a particular location within a vessel.
In a preferred embodiment, each of the inflatable channel members is disposed about the outer surface of a primary balloon. When the primary balloon is inflated, the inflatable channel members move outwardly, and preferably ultimately engage the vessel walls. After the primary balloon is inflated, selected inflatable channel members may be inflated with a radioactive fluid to irradiate the desired portion of a lesion. In preferred embodiments, the tubular member, having the lumen for carrying the radioactive fluid, is shielded so that users are not exposed to radiation over the length of the catheter, nor is the vessel lumen wall irradiated at areas other than the treatment site.
The primary balloon is preferably inflated with a non-radioactive fluid. Because the primary balloon occupies much of the cross-sectional area of the vessel when inflated, the amount of radioactive fluid required to fill the inflatable channel members is reduced relative to simply inflating the primary balloon with a radioactive fluid. Thus, the likelihood that a physician and/or a patient will become exposed to unnecessary radiation may be reduced, and the cost of obtaining and storing the radioactive fluid may likewise be reduced.
It is contemplated that the primary balloon may be of a size and type that can be used to perform an angioplasty procedure. That is, the primary balloon may be sized so that it may be positioned adjacent a restriction within a vessel, and of a type so that the restriction becomes dilated when the primary balloon is inflated. Because the inflatable channel members are preferably disposed about the outer surface of the primary balloon, the lesion at the site of treatment can be irradiated during or immediately after the angioplasty procedure. Alternatively, the primary balloon may be positioned across the treatment site after a conventional angioplasty catheter has been utilized to dilate then withdrawn. In either case, after a desired exposure period, the radioactive fluid may be withdrawn from the inflatable channel members, and the non-radioactive fluid may be withdrawn from the primary balloon. The device may then be withdrawn from the patient to complete the procedure.